1 ///////////////////////////////////////////////////////////////////////////////
2 //
3 /// \file       block_header_encoder.c
4 /// \brief      Encodes Block Header for .xz files
5 //
6 //  Author:     Lasse Collin
7 //
8 //  This file has been put into the public domain.
9 //  You can do whatever you want with this file.
10 //
11 ///////////////////////////////////////////////////////////////////////////////
12 
13 #include "common.h"
14 #include "check.h"
15 
16 
17 extern LZMA_API(lzma_ret)
18 lzma_block_header_size(lzma_block *block)
19 {
20 	if (block->version != 0)
21 		return LZMA_OPTIONS_ERROR;
22 
23 	// Block Header Size + Block Flags + CRC32.
24 	uint32_t size = 1 + 1 + 4;
25 
26 	// Compressed Size
27 	if (block->compressed_size != LZMA_VLI_UNKNOWN) {
28 		const uint32_t add = lzma_vli_size(block->compressed_size);
29 		if (add == 0 || block->compressed_size == 0)
30 			return LZMA_PROG_ERROR;
31 
32 		size += add;
33 	}
34 
35 	// Uncompressed Size
36 	if (block->uncompressed_size != LZMA_VLI_UNKNOWN) {
37 		const uint32_t add = lzma_vli_size(block->uncompressed_size);
38 		if (add == 0)
39 			return LZMA_PROG_ERROR;
40 
41 		size += add;
42 	}
43 
44 	// List of Filter Flags
45 	if (block->filters == NULL || block->filters[0].id == LZMA_VLI_UNKNOWN)
46 		return LZMA_PROG_ERROR;
47 
48 	for (size_t i = 0; block->filters[i].id != LZMA_VLI_UNKNOWN; ++i) {
49 		// Don't allow too many filters.
50 		if (i == LZMA_FILTERS_MAX)
51 			return LZMA_PROG_ERROR;
52 
53 		uint32_t add;
54 		return_if_error(lzma_filter_flags_size(&add,
55 				block->filters + i));
56 
57 		size += add;
58 	}
59 
60 	// Pad to a multiple of four bytes.
61 	block->header_size = (size + 3) & ~UINT32_C(3);
62 
63 	// NOTE: We don't verify that the encoded size of the Block stays
64 	// within limits. This is because it is possible that we are called
65 	// with exaggerated Compressed Size (e.g. LZMA_VLI_MAX) to reserve
66 	// space for Block Header, and later called again with lower,
67 	// real values.
68 
69 	return LZMA_OK;
70 }
71 
72 
73 extern LZMA_API(lzma_ret)
74 lzma_block_header_encode(const lzma_block *block, uint8_t *out)
75 {
76 	// Validate everything but filters.
77 	if (lzma_block_unpadded_size(block) == 0
78 			|| !lzma_vli_is_valid(block->uncompressed_size))
79 		return LZMA_PROG_ERROR;
80 
81 	// Indicate the size of the buffer _excluding_ the CRC32 field.
82 	const size_t out_size = block->header_size - 4;
83 
84 	// Store the Block Header Size.
85 	out[0] = out_size / 4;
86 
87 	// We write Block Flags in pieces.
88 	out[1] = 0x00;
89 	size_t out_pos = 2;
90 
91 	// Compressed Size
92 	if (block->compressed_size != LZMA_VLI_UNKNOWN) {
93 		return_if_error(lzma_vli_encode(block->compressed_size, NULL,
94 				out, &out_pos, out_size));
95 
96 		out[1] |= 0x40;
97 	}
98 
99 	// Uncompressed Size
100 	if (block->uncompressed_size != LZMA_VLI_UNKNOWN) {
101 		return_if_error(lzma_vli_encode(block->uncompressed_size, NULL,
102 				out, &out_pos, out_size));
103 
104 		out[1] |= 0x80;
105 	}
106 
107 	// Filter Flags
108 	if (block->filters == NULL || block->filters[0].id == LZMA_VLI_UNKNOWN)
109 		return LZMA_PROG_ERROR;
110 
111 	size_t filter_count = 0;
112 	do {
113 		// There can be a maximum of four filters.
114 		if (filter_count == LZMA_FILTERS_MAX)
115 			return LZMA_PROG_ERROR;
116 
117 		return_if_error(lzma_filter_flags_encode(
118 				block->filters + filter_count,
119 				out, &out_pos, out_size));
120 
121 	} while (block->filters[++filter_count].id != LZMA_VLI_UNKNOWN);
122 
123 	out[1] |= filter_count - 1;
124 
125 	// Padding
126 	memzero(out + out_pos, out_size - out_pos);
127 
128 	// CRC32
129 	unaligned_write32le(out + out_size, lzma_crc32(out, out_size, 0));
130 
131 	return LZMA_OK;
132 }
133